I get where you're coming from but I think there's a big difference between those two uses.

Googling symptoms of flu most likely means you think you have the flu and are using Google as a form of symptom checklist.

Googling stress relief methods could indicate you're stressed, or that you're doing research, curious, discussing different methods w friends & family, etc.

I don't think people are Googling "am I stressed (based on the following symptoms x y z)" - they already know they are - but they may not be sure whether they have the flu or a cold.

Correlation =/= causation.

Disappointing, though, because that's an interesting concept for a study - what factors contribute to stress and which areas of the country have the highest number of those factors.